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• Adding custom methods to a subclassed NSManagedObject

  - by CJ

  I have a Core Data model where I have an entity A, which is an abstract. Entities B, C, and D inherit from entity A. There are several properties defined in entity A which are used by B, C, and D. I would like to leverage this inheritance in my model code. In addition to properties, I am wondering if I can add methods to entity A, which are implemented in it's sub-entities. For example: I add a method to the interface for entity A which returns a value and takes one argument I add implementations of this method to A, B, C, D Then, I call executeFetchRequest: to retrieve all instances of B I call the method on the objects retrieved, which should call the implementation of the method contained in B's implementation I have tried this, but when calling the method, I receive: [NSManagedObject methodName:]: unrecognized selector sent to instance I presume this is because the objects returned by executeFetchRequest: are proxy objects of some sort. Is there any way to leverage inheritance using subclassed NSManagedObjects? I would really like to be able to do this, otherwise my model code would be responsible for determining what type of NSManagedObject it's dealing with and perform special logic according to the type, which is undesirable. Any help is appreciated, thanks in advance.

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• RIA Services for transmitting non DB object-graph

  - by Mike Gates

  I have been getting into RIA services because I thought it would simplify dealing with the services layer of web applications I wish to build. I see lots of examples out there showing how to create DomainService classes which expose and consume entities that have some kind of relational database backing, and therefore have foreign-key relationships. However, I would like to know how to expose and consume normal object graphs...objects that contain references to eachother but don't have foreign keys. For example, say I want a service operation called "GetFolderInformation(string pathToFolder)". I want this to return a custom object called "FolderInformation" structured with: - string Name - IEnumerable<FileInformation> Files I cannot get this to work because it seems that RIA wants to deal with entities that have foreign key relationships. Why? Why can't the serializer just see my object references and recreate that in the proxy on the other side? Data exists behind service layers that doesn't necessarily have foreign key relationships...like folder/file for example. EDIT: I realized I hadn't asked my question! My question is, is there a way to do what I am trying to do?

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• Design Decision - Scaling out web based application's architecture

  - by Vadi

  This question is about design decision. I am currently working on a web project that will have 40K users to start with and in couple of month expected to grow 50M users (not concurrent users though). I would like to have a architecture that can be scaled out easily without much effort. In order to explain, I would like to use a trivial scenario. Lets say, User entities and services such as CreateUser, AuthenticateUser etc., are a simple method calls for the Page Controllers. But once the traffic increases, for example, authenticating user (or such services related to user entities) has to be moved out to a different internal server to spread the load. But at the same time using RPC calls over the network when the user count is 40K would become overkill. My proposal was to use IPC initially and when we need to scale out we can interally switch to TCP based RPC calls so that it can easily scale out. For example, I am referring to System.IO.Pipes.NamedPipeStreamServer to start with and move on to a TcpListener later on. If we have proper design that can encapsulate above said approach, it would easy for us to scale out services into multiple network servers but at the same time avoid network calls when the user count is small. Is this is a best approach? Any suggestions would be great .. Note: The database scaling is definetly the second phase optimization so we have already made architectural design in place to easily partition data when traffic increases. The primary bottleneck would be application servers over the time period.

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• ASP.NET MVC - Binding a Child Entity to the Model

  - by Nathan Taylor

  This one seems painfully obvious to me, but for some reason I can't get it working the way I want it to. Perhaps it isn't possible the way I am doing it, but that seems unlikely. This question may be somewhat related: http://stackoverflow.com/questions/1274855/asp-net-mvc-model-binding-related-entities-on-same-page. I have an EditorTemplate to edit an entity with multiple related entity references. When the editor is rendered the user is given a drop down list to select related entities from, with the drop down list returning an ID as its value. <%=Html.DropDownListFor(m => m.Entity.ID)%> When the request is sent the form value is named as expected: "Entity.ID", however my strongly typed Model defined as an action parameter doesn't have Entity.ID populated with the value passed in the request. public ActionResult AddEntity(EntityWithChildEntities entityWithChildEntities) { } I tried fiddling around with the Bind() attribute and specified Bind(Include = "Entity.ID") on the entityWithChildEntities, but that doesn't seem to work. I also tried Bind(Include = "Entity"), but that resulted in the ModelBinder attempting to bind a full "Entity" definition (not surprisingly). Is there any way to get the default model binder to fill the child entity ID or will I need to add action parameters for each child entity's ID and then manually copy the values into the model definition?

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• Core data migration failing with "Can't find model for source store" but managedObjectModel for source is present

  - by Ira Cooke

  I have a cocoa application using core-data, which is now at the 4th version of its managed object model. My managed object model contains abstract entities but so far I have managed to get migration working by creating appropriate mapping models and creating my persistent store using addPersistentStoreWithType:configuration:options:error and with the NSMigratePersistentStoresAutomaticallyOption set to YES. NSDictionary *optionsDictionary = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:NSMigratePersistentStoresAutomaticallyOption]; NSURL *url = [NSURL fileURLWithPath: [applicationSupportFolder stringByAppendingPathComponent: @"MyApp.xml"]]; NSError *error=nil; [theCoordinator addPersistentStoreWithType:NSXMLStoreType configuration:nil URL:url options:optionsDictionary error:&error] This works fine when I migrate from model version 3 to 4, which is a migration that involves adding attributes to several entities. Now when I try to add a new model version (version 5), the call to addPersistentStoreWithType returns nil and the error remains empty. The migration from 4 to 5 involves adding a single attribute. I am struggling to debug the problem and have checked all the following; The source database is in fact at version 4 and the persistentStoreCoordinator's managed object model is at version 5. The 4-5 mapping model as well as managed object models for versions 4 and 5 are present in the resources folder of my built application. I've tried various model upgrade paths. Strangely I find that upgrading from an early version 3 - 5 works .. but upgrading from 4 - 5 fails. I've tried adding a custom entity migration policy for migration of the entity whose attributes are changing ... in this case I overrode the method beginEntityMapping:manager:error: . Interestingly this method does get called when migration works (ie when I migrate from 3 to 4, or from 3 to 5 ), but it does not get called in the case that fails ( 4 to 5 ). I'm pretty much at a loss as to where to proceed. Any ideas to help debug this problem would be much appreciated.

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• How to make an entity out of a join table without primary key

  - by tputkonen

  I'm trying to generate JPA entities out of an existing database having an "interesting" design. Database has a table called UserSet, which can have links to several other UserSets. There is a one to many relation between UserSets and LinkedUserSets. LinkedUserSets also has one to one relation to UserSets. I tried to generate a JPA Entity out of the database structure using Dali JPA Tools. The resulting entity Linkeduserset misses @Id or @EmbeddedId annotation and thus failes to compile. As the resulting entity contains only two @JoinColumns (which cannot be marked as @Id), I have not so far found a way around this issue. Database structure can not be modified in any way. Is there a way to overcome this somehow? Relevant pars of create table statements: CREATE TABLE `LinkedUserSets` ( `UsrSetID` INT(11) NOT NULL DEFAULT '0' , `ChildID` INT(11) NOT NULL DEFAULT '0' , CONSTRAINT `fk_LinkedUserSets_UserSet1` FOREIGN KEY (`UsrSetID` ) REFERENCES `UserSet` (`UsrSetID` )); CREATE TABLE `UserSet` ( `UsrSetID` INT(11) NOT NULL AUTO_INCREMENT , PRIMARY KEY (`UsrSetID`), CONSTRAINT `fk_UserSet_LinkedUserSets1` FOREIGN KEY (`UsrSetID` ) REFERENCES `LinkedUserSets` (`ChildID` )); Generated entities: @Entity @Table(name="linkedusersets") public class Linkeduserset { //bi-directional many-to-one association to Userset @ManyToOne @JoinColumn(name="UsrSetID") private Userset userset1; //bi-directional one-to-one association to Userset @OneToOne @JoinColumn(name="ChildID") private Userset userset2; } @Entity @Table(name="userset") public class Userset { private static final long serialVersionUID = 1L; @Id @Column(name="UsrSetID") private int jngSetID; //bi-directional many-to-one association to Linkeduserset @OneToMany(mappedBy="userset1") private Set<Linkeduserset> linkedusersets; //bi-directional one-to-one association to Linkeduserset @OneToOne(mappedBy="userset2") private Linkeduserset linkeduserset; } Error message: Entity "Linkeduserset" has no Id or EmbeddedId

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• NHibernate stored procedure problem

  - by Calvin

  I'm having a hard time trying to get my stored procedure works with NHibernate. The data returned from the SP does not correspond to any database table. This is my mapping file: <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="DomainModel" namespace="DomainModel.Entities"> <sql-query name="DoSomething"> <return class="SomeClass"> <return-property name="ID" column="ID"/> </return> exec [dbo].[sp_doSomething] </sql-query> </hibernate-mapping> Here is my domain class: namespace DomainModel.Entities { public class SomeClass { public SomeClass() { } public virtual Guid ID { get; set; } } } When I run the code, it fails with Exception Details: NHibernate.HibernateException: Errors in named queries: {DoSomething} at line 80 Line 78: config.Configure(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "NHibernate.config")); Line 79: Line 80: g_sessionFactory = config.BuildSessionFactory(); When I debug into NHibernate code, it seems that SomeClass is not added to the persister dictionary because there isn't a class mapping (only sql-query) defined in hbm.xml. And later on in CheckNamedQueries function, it is not able to find the persistor for SomeClass. I've checked all the obvious things (e.g. make hbm as an embedded resource) and my code isn't too much different from other samples I found on the web, but somehow I just can't get it working. Any idea how I can resolve this issue?

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• C# POCO T4 template, generate interfaces?

  - by Jonna

  Does anyone know of any tweaked version of POCO T4 template that generates interfaces along with classes? i.e. if I have Movie and Actor entities in .edmx file, I need to get the following classes and interfaces. interface IMovie { string MovieName { get; set; } ICollection<IActor> Actors { get; set; } //instead of ICollection<Actor> } class Movie : IMovie { string MovieName { get; set; } ICollection<IActor> Actors { get; set; } //instead of ICollection<Actor> } interface IActor { string ActorName { get; set; } } class Actor { string ActorName { get; set; } } Also, just in case I write my own entities, does POCO proxies(I need them for lazy loading) work with the interface declarations as shown above?

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• Entity Framework - refresh objects from database

  - by Nebo

  I'm having trouble with refreshing objects in my database. I have an two PC's and two applications. On the first PC, there's an application which communicates with my database and adds some data to Measurements table. On my other PC, there's an application which retrives the latest Measurement under a timer, so it should retrive measurements added by the application on my first PC too. The problem is it doesn't. On my application start, it caches all the data from database and never get new data added. I use Refresh() method which works well when I change any of the cached data, but it doesn't refresh newly added data. Here is my method which should update the data: public static Entities myEntities = new Entities(); public static Measurement GetLastMeasurement(int conditionId) { myEntities.Refresh(RefreshMode.StoreWins, myEntities.Measurements); return (from measurement in myEntities.Measurements where measurement.ConditionId == conditionId select measurement).OrderByDescending(cd => cd.Timestamp).First(); } P.S. Applications have different connection strings in app.config (different accounts for the same DB).

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• Is it possible to add JPA annotation to superclass instance variables?

  - by Kristofer Borgstrom

  Hi, I am creating entities that are the same for two different tables. In order do table mappings etc. different for the two entities but only have the rest of the code in one place - an abstract superclass. The best thing would be to be able to annotate generic stuff such as column names (since the will be identical) in the super class but that does not work because JPA annotations are not inherited by child classes. Here is an example: public abstract class MyAbstractEntity { @Column(name="PROPERTY") //This will not be inherited and is therefore useless here protected String property; public String getProperty() { return this.property; } //setters, hashCode, equals etc. methods } Which I would like to inherit and only specify the child-specific stuff, like annotations: @Entity @Table(name="MY_ENTITY_TABLE") public class MyEntity extends MyAbstractEntity { //This will not work since this field does not override the super class field, thus the setters and getters break. @Column(name="PROPERTY") protected String property; } Any ideas or will I have to create fields, getters and setters in the child classes? Thanks, Kris

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• Entity Framework. Updating EntityCollection using disconnected objects via navigation property.

  - by yougotiger

  I have a question, much liket this unanswered one. I'm trying to work with the entity framework, and having a tough time getting my foreign tables to update. I have something basically like this in the DB: Incident (table): -ID -other fields Responses (table): -FK:Incident.ID -other fields And and entities that match: Incident (entity) -ID -Other fields -Responses (EntityCollection of Responses via navigation property) Each Incident can have 0 or more responses. In my Webpage, I have a form to allow the user to enter all the details of an Incident, including a list of responses. I can add everything to the database when a new Incident is created, however I'm having difficulty with editing the Incident. When the page loads for edit, I populate the form and then store the responses in the viewstate. When the user changes the list of responses (adds one, deletes one or edits one). I store this back into the viewstate. Then when the user clicks the save button, I'd like to save the changes to the Incident and the Responses back to the DB. I cannot figure out how to get the responses from the detached viewstate into the Incident object so that they can be updated together. Currently when the user clicks save, I'm getting the Incident to edit from the db, making changes to the Incident's fields and then saving it back to the DB. However I can't figure out how to have the detached list of responses from the viewstate attach to the Incident. I have tried the following without success: Clearning the Incident.Responses collection and adding the ones from the viewstate back in: Incident.Responses.Clear() for each objResponse in Viewstate("Responses") Incident.Responses.add(objResponse) next Creating an EntityCollection from my list and then assiging that to the Incident.Responses Incident.Responses = EntityCollectionFromViewstateList Iterating through the responses in Incident.Response and assigning the corresponding object from viewstate: for each ObjResponse in Incident.Responses objResponse = objCorrespondingModifedResonseFromViewState Next These all fail, I'd like to be able to merge the changes into the Inicdent object so that when the BLL calls SaveChanges on the changes to both the Incident and Responses will happen at the same time. Any suggestions? I keep finding lots of stuff about assigning foreign keys (singular), but I haven't found a great solution for doing a set of entities assigned to another entity in this manner.

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• GAE datastore querying integer fields

  - by ParanoidAndroid

  I notice strange behavior when querying the GAE datastore. Under certain circumstances Filter does not work for integer fields. The following java code reproduces the problem: log.info("start experiment"); DatastoreService datastore = DatastoreServiceFactory.getDatastoreService(); int val = 777; // create and store the first entity. Entity testEntity1 = new Entity(KeyFactory.createKey("Test", "entity1")); Object value = new Integer(val); testEntity1.setProperty("field", value); datastore.put(testEntity1); // create the second entity by using BeanUtils. Test test2 = new Test(); // just a regular bean with an int field test2.setField(val); Entity testEntity2 = new Entity(KeyFactory.createKey("Test", "entity2")); Map<String, Object> description = BeanUtilsBean.getInstance().describe(test2); for(Entry<String,Object> entry:description.entrySet()){ testEntity2.setProperty(entry.getKey(), entry.getValue()); } datastore.put(testEntity2); // now try to retrieve the entities from the database... Filter equalFilter = new FilterPredicate("field", FilterOperator.EQUAL, val); Query q = new Query("Test").setFilter(equalFilter); Iterator<Entity> iter = datastore.prepare(q).asIterator(); while (iter.hasNext()) { log.info("found entity: " + iter.next().getKey()); } log.info("experiment finished"); the log looks like this: INFO: start experiment INFO: found entity: Test("entity1") INFO: experiment finished For some reason it only finds the first entity even though both entities are actually stored in the datastore and both 'field' values are 777 (I see it in the Datastore Viewer)! Why does it matter how the entity is created? I would like to use BeanUtils, because it is convenient. The same problem occurs on the local devserver and when deployed to GAE.

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• Organizing Eager Queries in an ObjectContext

  - by Nix

  I am messing around with Entity Framework 3.5 SP1 and I am trying to find a cleaner way to do the below. I have an EF model and I am adding some Eager Loaded entities and i want them all to reside in the "Eager" property in the context. We originally were just changing the entity set name, but it seems a lot cleaner to just use a property, and keep the entity set name in tact. Example: Context - EntityType - AnotherType - Eager (all of these would have .Includes to pull in all assoc. tables) - EntityType - AnotherType Currently I am using composition but I feel like there is an easier way to do what I want. namespace Entities{ public partial class TestObjectContext { EagerExtensions Eager { get;set;} public TestObjectContext(){ Eager = new EagerExtensions (this); } } public partial class EagerExtensions { TestObjectContext context; public EagerExtensions(TestObjectContext _context){ context = _context; } public IQueryable<TestEntity> TestEntity { get { return context.TestEntity .Include("TestEntityType") .Include("Test.Attached.AttachedType") .AsQueryable(); } } } } public class Tester{ public void ShowHowIWantIt(){ TestObjectContext context= new TestObjectContext(); var query = from a in context.Eager.TestEntity select a; } }

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• How can I make this LinqToSQL query work? (SqlExecption)

  - by kversch

  The following code gives me an SqlException: OO theCourse = subject.Course; var students = dc.studentsCourses.Where(x = x.course == theCourse).Select(x = x.student); "Invalid object name 'dbo.studentsCourses'." I tried the following code instead but I also get an Exception. My original question was asked on Aardvark and can be read bellow: var allStudents = from s in dc.students select s; List thestudents = new List(); foreach (student s in allStudents) { if (s.courses.Contains(theCourse)) { thestudents.Add(s); } } I did a right click, "run custom tool" on my dbml and checked my names of my tables and entities. The project compiles but I get an Exception at runtime on this line: "if (s.courses.Contains(theCourse))" Any ideas? Original question on Aardvark: How do I do a LinqToSQL query that gives me this: I want to select all students that attended a certain lesson. The lesson is from a certain course. So select the course the lesson is from. Now select all the students that are following that course. There is a many-to-many relationship between the students and the courses table in my DB. I already extended my LINQ entities to be able to select student.Courses and course.Students using this method: http://www.codeproject.com/KB/linq/linq-to-sql-many-to-many.aspx

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• Emptying the datastore in GAE

  - by colwilson

  I know what you're thinking, 'O not that again!', but here we are since Google have not yet provided a simpler method. I have been using a queue based solution which worked fine: import datetime from models import * DELETABLE_MODELS = [Alpha, Beta, AlphaBeta] def initiate_purge(): for e in config.DELETABLE_MODELS: deferred.defer(delete_entities, e, 'purging', _queue = 'purging') class NotEmptyException(Exception): pass def delete_entities(e, queue): try: q = e.all(keys_only=True) db.delete(q.fetch(200)) ct = q.count(1) if ct > 0: raise NotEmptyException('there are still entities to be deleted') else: logging.info('processing %s completed' % queue) except Exception, err: deferred.defer(delete_entities, e, then, queue, _queue = queue) logging.info('processing %s deferred: %s' % (queue, err)) All this does is queue a request to delete some data (once for each class) and then if the queued process either fails or knows there is still some stuff to delete, it re-queues itself. This beats the heck out of hitting the refresh on a browser for 10 minutes. However, I'm having trouble deleting AlphaBeta entities, there are always a few left at the end. I think because it contains Reference Properties: class AlphaBeta(db.Model): alpha = db.ReferenceProperty(Alpha, required=True, collection_name='betas') beta = db.ReferenceProperty(Beta, required=True, collection_name='alphas') I have tried deleting the indexes relating to these entity types, but that did not make any difference. Any advice would be appreciated please.

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• [Database] How to model this one-to-one relation?

  - by pbean

  I have several entities which respresent different types of users who need to be able to log in to a particular system. Additionally, they have different types of information associated with them. For example: a "general user", which has an e-mail address and "admin user", which has a workstation number (note that this a hypothetical case). Both entities also share common properties like first name, surname, address and telephone number. Finally, they naturally need to have a (unique) user name and a password to log in. In the application, the user just has to fill in his user name and password, and the functionality of the application changes slightly according to the type of the user. You can imagine that the username needs to be unique for this work. How should I model this effectively? I can't just create two tables, because then I can't force a unique constaint on the user name. I also can't put them all in just one table, because they have different types of specific information associated to them. I think I might need 3 seperate tables, one for "users" (with user name and password), one for the "general users" and another one for the "admin users", but how would the relations between these work? Or is there another solution? (By the way, the target DBMS is MySQL, so I don't think generalization is supported in the database system itself).

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• Reverse mapping from a table to a model in SQLAlchemy

  - by Jace

  To provide an activity log in my SQLAlchemy-based app, I have a model like this: class ActivityLog(Base): __tablename__ = 'activitylog' id = Column(Integer, primary_key=True) activity_by_id = Column(Integer, ForeignKey('users.id'), nullable=False) activity_by = relation(User, primaryjoin=activity_by_id == User.id) activity_at = Column(DateTime, default=datetime.utcnow, nullable=False) activity_type = Column(SmallInteger, nullable=False) target_table = Column(Unicode(20), nullable=False) target_id = Column(Integer, nullable=False) target_title = Column(Unicode(255), nullable=False) The log contains entries for multiple tables, so I can't use ForeignKey relations. Log entries are made like this: doc = Document(name=u'mydoc', title=u'My Test Document', created_by=user, edited_by=user) session.add(doc) session.flush() # See note below log = ActivityLog(activity_by=user, activity_type=ACTIVITY_ADD, target_table=Document.__table__.name, target_id=doc.id, target_title=doc.title) session.add(log) This leaves me with three problems: I have to flush the session before my doc object gets an id. If I had used a ForeignKey column and a relation mapper, I could have simply called ActivityLog(target=doc) and let SQLAlchemy do the work. Is there any way to work around needing to flush by hand? The target_table parameter is too verbose. I suppose I could solve this with a target property setter in ActivityLog that automatically retrieves the table name and id from a given instance. Biggest of all, I'm not sure how to retrieve a model instance from the database. Given an ActivityLog instance log, calling self.session.query(log.target_table).get(log.target_id) does not work, as query() expects a model as parameter. One workaround appears to be to use polymorphism and derive all my models from a base model which ActivityLog recognises. Something like this: class Entity(Base): __tablename__ = 'entities' id = Column(Integer, primary_key=True) title = Column(Unicode(255), nullable=False) edited_at = Column(DateTime, onupdate=datetime.utcnow, nullable=False) entity_type = Column(Unicode(20), nullable=False) __mapper_args__ = {'polymorphic_on': entity_type} class Document(Entity): __tablename__ = 'documents' __mapper_args__ = {'polymorphic_identity': 'document'} body = Column(UnicodeText, nullable=False) class ActivityLog(Base): __tablename__ = 'activitylog' id = Column(Integer, primary_key=True) ... target_id = Column(Integer, ForeignKey('entities.id'), nullable=False) target = relation(Entity) If I do this, ActivityLog(...).target will give me a Document instance when it refers to a Document, but I'm not sure it's worth the overhead of having two tables for everything. Should I go ahead and do it this way?

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• How to determine one to many column name from entity type

  - by snicker

  I need a way to determine the name of the column used by NHibernate to join one-to-many collections from the collected entity's type. I need to be able to determine this at runtime. Here is an example: I have some entities: namespace Entities { public class Stable { public virtual int Id {get; set;} public virtual string StableName {get; set;} public virtual IList<Pony> Ponies { get; set; } } public class Dude { public virtual int Id { get; set; } public virtual string DudesName { get; set; } public virtual IList<Pony> PoniesThatBelongToDude { get; set; } } public class Pony { public virtual int Id {get; set;} public virtual string Name {get; set;} public virtual string Color { get; set; } } } I am using NHibernate to generate the database schema, which comes out looking like this: create table "Stable" (Id integer, StableName TEXT, primary key (Id)) create table "Dude" (Id integer, DudesName TEXT, primary key (Id)) create table "Pony" (Id integer, Name TEXT, Color TEXT, Stable_id INTEGER, Dude_id INTEGER, primary key (Id)) Given that I have a Pony entity in my code, I need to be able to find out: A. Does Pony even belong to a collection in the mapping? B. If it does, what are the column names in the database table that pertain to collections In the above instance, I would like to see that Pony has two collection columns, Stable_id and Dude_id.

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• Java object graph -> xml when direction of object association needs to be reversed.

  - by Sigmoidal

  An application I have been working on has objects with a relationship similar to below. In the real application both objects are JPA entities. class Underlying{} class Thing { private Underlying underlying; public Underlying getUnderlying() { return underlying; } public void setUnderlying(final Underlying underlying) { this.underlying = underlying; } } There is a requirement in the application to create xml of the form: <template> <underlying> <thing/> <thing/> <thing/> </underlying> </template> So we have a situation where the object graph expresses the relationship between Thing and Underlying in the opposite direction to how it's expressed in the xml. I expect to use JAXB to create the xml but ideally I don't want to have to create a new object hierarchy to reflect the associations in the xml. Is there any way to create xml of the form required from the entities in their current form (through the use of xml annotations or something)? I don't have any experience using JAXB but from the limited research I've done it doesn't seem like it's possible to reverse the direction of association in any straightforward way. Any help/advice would be greatly appreciated. One other option that has been suggested is to use XLST to transform the xml into the correct format. I have done no research on this topic as yet but I'll add to the question when I have some more info. Thanks, Matt.

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• Multi-Column Join in Hibernate/JPA Annotations

  - by bowsie

  I have two entities which I would like to join through multiple columns. These columns are shared by an @Embeddable object that is shared by both entities. In the example below, Foo can have only one Bar but Bar can have multiple Foos (where AnEmbeddableObject is a unique key for Bar). Here is an example: @Entity @Table(name = "foo") public class Foo { @Id @Column(name = "id") @GeneratedValue(generator = "seqGen") @SequenceGenerator(name = "seqGen", sequenceName = "FOO_ID_SEQ", allocationSize = 1) private Long id; @Embedded private AnEmbeddableObject anEmbeddableObject; @ManyToOne(targetEntity = Bar.class, fetch = FetchType.LAZY) @JoinColumns( { @JoinColumn(name = "column_1", referencedColumnName = "column_1"), @JoinColumn(name = "column_2", referencedColumnName = "column_2"), @JoinColumn(name = "column_3", referencedColumnName = "column_3"), @JoinColumn(name = "column_4", referencedColumnName = "column_4") }) private Bar bar; // ... rest of class } And the Bar class: @Entity @Table(name = "bar") public class Bar { @Id @Column(name = "id") @GeneratedValue(generator = "seqGen") @SequenceGenerator(name = "seqGen", sequenceName = "BAR_ID_SEQ", allocationSize = 1) private Long id; @Embedded private AnEmbeddableObject anEmbeddableObject; // ... rest of class } Finally the AnEmbeddedObject class: @Embeddable public class AnEmbeddedObject { @Column(name = "column_1") private Long column1; @Column(name = "column_2") private Long column2; @Column(name = "column_3") private Long column3; @Column(name = "column_4") private Long column4; // ... rest of class } Obviously the schema is poorly normalised, it is a restriction that AnEmbeddedObject's fields are repeated in each table. The problem I have is that I receive this error when I try to start up Hibernate: org.hibernate.AnnotationException: referencedColumnNames(column_1, column_2, column_3, column_4) of Foo.bar referencing Bar not mapped to a single property I have tried marking the JoinColumns are not insertable and updatable, but with no luck. Is there a way to express this with Hibernate/JPA annotations? Thank you.

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• How to properly use Object Contexts in Entity Framework using BackgroundWorker

  - by OffApps Cory

  Good day, I am developing using Entity Framework and WPF, and I am encountering some errors and I don't know why. When saving a record (using a BackgroundWorker), I set the entities change tracker to nothing (null), attach the record to a new disposable context, save it, detach, and dispose of the context. Saving a record fires and event in the MainViewModel of the program that the other ViewModels (including the one that is saving) need to refresh their entities to reflect changes. Private Sub _saveRecordWorker_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles _saveRecordWorker.DoWork Using MyContext As New RVShippingEntities Dim MyShipment = CType(ShipmentRecord, IEntityWithChangeTracker) MyShipment.SetChangeTracker(Nothing) MyContext.Attach(MyShipment) MyContext.Detach(ShipmentRecord) End Using End Sub The Refresh background worker is similar, but it has a Do While block to keep it from interfering with the save worker (which doesn't appear to be working; hence the post). When I save (and it subsequently refreshes) I get the following error: The calling thread cannot access this object because a different thread owns it. I thought that with the DoWhile block, it would wait (and when i step through it does) until the save thread finished, and all would be good. But it would seem that something (either the main thread or the save thread) is still doing something that is interfering. Is there a better way of doing this? Am I doing it is a goofy kludgey fashion? Any help would be appreciated. (Apparently Firefox recognized kludgey as a word. Interesting)

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• Updating entity fields in app engine development server

  - by Joey

  I recently tried updating a field in one of my entities on the app engine local dev server via the sdk console. It appeared to have updated just fine (a simple float). However, when I followed up with a query on the entity, I received an exception: "Items in the mSomeList list must all be Key instances". mSomeList is just another list field I have in that entity, not the one I modified. Is there any reason manually changing a field would adversely throw something off such that the server gets confused? Is this a known bug? I wrote an http handler to alter the field through server code and it works fine if I take that approach. Update: (adding details) I am using the python google app engine server. Basically if I go into the Google App Engine Launcher and press the SDK Console button, then go into one of my entities and edit a field that is a float (i.e. change it from 0 to 3.5, for instance), I get the "Items in the mMyList list must all be Key instance" suddenly when I query the entity like this: query = DataModels.RegionData.gql("WHERE mRegion = :1", region) entry = query.get() the RegionData entity is what has the mMyList member. As mentioned previously, if I do not manually change the field but rather do so through server code, i.e. query = DataModels.RegionData.gql("WHERE mRegion = :1", region) entry = query.get() entry.mMyFloat = 3.5 entry.put() Then it works.

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• Architecting ASP.net MVC App to use repositories and services

  - by zaladane

  Hello, I recently started reading about ASP.net MVC and after getting excited about the concept, i started to migrate all my webform project to MVC but i am having a hard time keeping my controller skinny even after following all the good advices out there (or maybe i just don't get it ... ). The website i deal with has Articles, Videos, Quotes ... and each of these entities have categories, comments, images that can be associated with it. I am using Linq to sql for database operations and for each of these Entities, i have a Repository, and for each repository, i create a service to be used in the controller. so i have - ArticleRepository ArticleCategoryRepository ArticleCommentRepository and the corresponding service ArticleService ArticleCategoryService ... you see the picture. The problem i have is that i have one controller for article,category and comment because i thought that having ArticleController handle all of that might make sense, but now i have to pass all of the services needed to the Controller constructor. So i would like to know what it is that i am doing wrong. Are my services not designed properly? should i create Bigger service to encapsulate smaller services and use them in my controller? or should i have an articleCategory Controller and an articleComment Controller? A page viewed by the user is made of all of that, thee article to be viewed,the comments associated with it, a listing of the categories to witch it applies ... how can i efficiently break down the controller to keep it "skinny" and solve my headache? Thank you! I hope my question is not too long to be read ...

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• Using EhCache for session.createCriteria(...).list()

  - by James Smith

  I'm benchmarking the performance gains from using a 2nd level cache in Hibernate (enabling EhCache), but it doesn't seem to improve performance. In fact, the time to perform the query slightly increases. The query is: session.createCriteria(MyEntity.class).list(); The entity is: @Entity @Cache(usage = CacheConcurrencyStrategy.NONSTRICT_READ_WRITE) public class MyEntity { @Id @GeneratedValue private long id; @Column(length=5000) private String data; //---SNIP getters and setters--- } My hibernate.cfg.xml is: <!-- all the normal stuff to get it to connect & map the entities plus:--> <property name="hibernate.cache.region.factory_class"> net.sf.ehcache.hibernate.EhCacheRegionFactory </property> The MyEntity table contains about 2000 rows. The problem is that before adding in the cache, the query above to list all entities took an average of 65 ms. After the cache, they take an average of 74 ms. Is there something I'm missing? Is there something extra that needs to be done that will increase performance?

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• Entity Framework and WCf

  - by Nihilist

  Hi I am little confused on designing WCf services with EF. When using WCf and EF, where do we draw this line on what properties to return and what not to with the entity. Here is my scenario I have User. Here are the relations. User [1 to many] Address, User [ 1 to many] Email, User [ 1 to many] Phone So now on the webform, on page1 I can edit user information. say I can edit few properties on the user entity and can also edit address, phone, email entities[ like add / delete and update any] On page2, i can only update user properties and nothing related to navigation properties [ address, email, phone]. So when I return the User Entity [ OR DTO] should i be returning the navigation properties too? Or should the client make multiple calls to get navigation properites. Also, how does it go with Save? Like should the client make multiple calls to save user and related entites or just one call to save the graph? Lets say, if I just have a Save(User user) [ where user has all the related entities too] both page1 and page2 will call save and pass me the user. but one page1 i will need a lot more information. but on page2 i just need the user primitive properties. So my question is, where do we draw this line, how do we design theses services ? Is the WCF operation designed on the page and the fields it has ? I am hoping i explained my problem well enough.

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